Head positioning control method and device for storage disk apparatus

ABSTRACT

In a head positioning method and device in which the position of position signals between heads is not uniform, it is aimed to reduce the time taken to find the position signals even when heads are switched. The storage disk device comprises a storage disk  1  with the position signal, a plurality of heads  3   a  through  3   d  that read the information from recording disk  1 , an actuator  5  that moves the heads, and a control circuit  11  that positions the heads based on the position signals read from the recording disk by the selected head. This control circuit  11  comprises a synchronization circuit  6  that, in response to a head switching cue, synchronizes the time of the detection signal for detecting the position signal with the time of the position signal read by the head to which switching is directed, and a processing circuit  11  that reads the position signal for the head in response to the synchronized detection signal and positions the head in response to the position signal read.

FIELD OF THE INVENTION

[0001] The present invention relates to a head positioning controlmethod and device that reads a positioning signal of a storage disk andpositions a head in a storage disk apparatus that uses the head to readinformation from or read/write information from/to the storage disk andmore particularly to a head positioning control method and device for astorage disk device with a plurality of heads.

DESCRIPTION OF THE RELATED ART

[0002] Storage disk devices, such as magnetic disk devices, are widelyused as storage devices in computers. In these types of storage diskdevices, the format of the storage disk is divided into sectors. Servosignals (position signals) are recorded onto these sectors. The headreads these servo signals and is positioned at the centre of a track.High-density recording is required in these types of storage diskdevices.

[0003]FIG. 12 is a schematic view of the conventional art, FIG. 13 is arelational view of conventional servo signals, and FIG. 14 is arelational view of other conventional servo signals.

[0004] As shown in FIG. 12, a magnetic disk device has a magnetic disk90 and magnetic heads 91-a through 91-d. Servo signals (positionsignals) are recorded for each sector on the magnetic disk 90. Magneticheads 91-a through 91-d read information from and write information tothe magnetic disk 90. The spindle motor 92 rotates the magnetic disk 90.The voice coil motor 93 positions the magnetic heads 91-a through 91-d.

[0005] The servo signal demodulator detects the servo signal from theread output of magnetic heads 91-a through 91-d in response to a servogate signal and demodulates the servo signal into a position signal. Theread-write circuit 96, demodulates read data from the output read fromthe magnetic heads 91-a through 91-d and supplies write data to magneticheads 91-a through 91-d.

[0006] The control circuit 95 calculates the current head position inresponse to the demodulated position signal and creates a drive valuefor the voice coil motor 93. That is, during seek control (coarsecontrol), the control circuit 94 calculates the current position fromthe position signal and creates a current indication value in responseto the distance seek moves. Also, while on track (during fine control),the control circuit 95 determines the deviation from the centre of thetrack from the position signal and creates a current indication value.

[0007] In this type of servo control system, a servo signal is recordedonto each sector of the magnetic disk 90 so that the positions ofmagnetic heads 91-a through 91-d can be detected. When a device isequipped with a plurality of magnetic heads, positioning is controlledusing servo signals read by the read/write head to be selected.

[0008]FIG. 13 shows the timing of the servo signals Sv from each headwhen the heads reproduce the signals. A servo signal SV is actually onlyread in one head but here, to show the servo signal Sv timing for eachhead, servo signals from all heads are shown for convenience.

[0009] As shown in FIG. 13, the servo signals SV read by each head 0through 2 (91-a through 91-c) are produced with the same timing. Forexample, when head 0 is switched over to head 1, the time when the servosignal SV is read does not change. That is, the position signals foreach head exist at the same time. Therefore, the servo gate signal fordetecting the servo signal is produced at the same time regardless ofthe head involved.

[0010]FIG. 14 shows the method called the staggered sector for recordingservo signals Sv. The times when the servo signals SV for each head arewritten are staggered in constant time intervals T1. This method enablesheads to be sequentially selected and the servo signal to besequentially written when a servo signal is written to a magnetic disk.Accordingly, the servo signals can be written rapidly. In this method,the times at which servo gate signals, which detect the servo signals,are produced are staggered using a constant interval.

[0011] Thus, in the conventional art, the timing of servo gate signalsfor detecting servo signals in each head is the same or staggered usinga constant interval.

[0012]FIG. 15 explains the problems with the conventional art.

[0013] The study is done concerning the assembly of a magnetic disk intothe device after the servo signals are recorded onto the magnetic disk.In comparison to the method of recording servo signals after themagnetic disk is assembled into the device, this method would enablehigher-density recording of servo signals.

[0014] That is, the voice coil motor in the magnetic disk device isrequired to move quickly. It is difficult to demand high-densitypositioning accuracy of this voice coil motor. Therefore, magnetic diskservo signals are written using a high-accuracy servo-writing deviceoutside the device. The magnetic disk that writes the servo signals isthen mounted onto the device.

[0015] This enables highly accurate recording of servo signals andhigh-density recording in the magnetic disk device. However as shown inFIG. 15, when a magnetic disk that has recorded servo signals ismounted, the servo signal SV period Ts for each head is constant, butthe time intervals for servo signals between heads differ.

[0016] That is, the slight discrepancies in the positions of each headin the magnetic disk device, the slight discrepancies in the positionsof the external write head and the internal read head, and the slightdiscrepancy in the mounting position of each magnetic disk cause theservo signal time interval between heads to vary. In FIG. 15, the timeinterval T1 between head 0 and head 1 is different to the time intervalT2 between head 2 and head 0.

[0017] Therefore, the servo signal must be sought when the heads areswitched over causing the problem of a long time being required forswitching heads.

SUMMARY OF THE INVENTION

[0018] An object of the present invention is to provide a headpositioning control method and device for a storage disk apparatus toenable a reduction in the head switching time even when the servo signaltime changes for each head.

[0019] A further object of the present invention is to provide a headpositioning control method and device for a recording disk apparatusthat does not require a search for the servo signals even when the servosignal time changes for each head.

[0020] A still further object of the present invention is to provide ahead positioning control method and device for a recording diskapparatus that will synchronize servo gate signals with servo signalseven when the servo signal time changes for each head.

[0021] In an aspect of the present invention, the storage disk apparatuscomprises a storage disk for recording position signals, a plurality ofheads for reading information on the storage disk, an actuator formoving the heads, and a control circuit that positions the heads basedon position signals read from the storage disk by the selected head.

[0022] This head positioning control method comprises a step forsynchronizing the time of a detection signal for detecting a positionsignal with the time of a position signal that is read by the head towhich switching is directed in response to a head switching cue, and astep of reading a head position signal in response to the synchronizeddetection signals and positioning the head in response to the readposition signal.

[0023] The present invention synchronizes the time at which a detectionsignal is produced with the time of the position signal for the head towhich switching is directed in response to a head switching cue. Thismeans that because the time at which the detection signal is generatedis synchronized with the time of the position signal for the head towhich switching is directed, that position signal can be detected evenif the operation to find the position signal at the time head switchingoccurs is omitted. Therefore, the head switching time can be reduced andfast head switching enabled.

[0024] Also, in another aspect of the present invention, thesynchronization step comprises a step for determining the time at whichthe position signal is read by the head to which switching is directedin response to the head switching cue, and a step for synchronizing thetime of the detection signal with that determined time.

[0025] In still another aspect of the present invention, the timedetermining step comprises a step for determining above time so that thetime value is greater than a single sample period in positioningcontrol.

[0026] In still another aspect of the present invention, the timedetermining step includes a step for reading the time at which the headto which the above switching is directed from the memory in which arestored the times that position signals are read from each head.

[0027] In still another aspect of the present invention, the timedetermining step is a step for determining the time difference betweenthe time of detection of the above position signal for the head at whichswitching originates and the time of detection of the above positionsignal for the head to which the above switching is directed.Furthermore, the synchronizing step comprises a step that shifts in timethe above detection signal by that time difference.

[0028] In still another aspect of the present invention, the timedetermining step comprises a step for determining the detection time forthe position signal of the head prior to switching, a step fordetermining the detection time for the said position signal of the headto which switching is directed, and a step for determining the timedifference between the two times.

[0029] In still another aspect of the present invention, the positioningstep comprises a step for determining the time difference between thedetection time for the head prior to the above switching in done inresponse to a head switching cue and the detection time for the head towhich switching is directed, a step for determining whether or not thetime difference is shorter than the interval for one sample, and a stepfor inhibiting positioning in response to above detection signal whenthe time difference is shorter than the interval for one sample.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a block diagram of an aspect of the embodiment of thepresent invention;

[0031]FIG. 2 is a block diagram of the position detection circuit ofFIG. 1;

[0032]FIG. 3 explains the servo signal of FIG. 1;

[0033]FIG. 4 is a flowchart showing the head switching process of FIG.2;

[0034]FIG. 5 explains the head switching operation of FIG. 2;

[0035]FIG. 6 is a relational view of servo gate signals in a secondaspect of the embodiment of the present invention;

[0036]FIG. 7 is a block diagram of a third aspect of the embodiment ofthe present invention;

[0037]FIG. 8 is a flowchart showing the processing of a fourth aspect ofthe embodiment of the present invention;

[0038]FIG. 9 is a block diagram of different time measurements betweenheads in the present invention;

[0039]FIG. 10 is a flowchart showing the processing of the differenttimes between heads in the present invention;

[0040]FIG. 11 explains a fifth aspect of the embodiment of the presentinvention;

[0041]FIG. 12 is a schematic view of the conventional art;

[0042]FIG. 13 is a relational view of conventional servo signals;

[0043]FIG. 14 is a relational view of other conventional servo signals;and

[0044]FIG. 15 explains problems with the conventional art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045]FIG. 1 is a block diagram of an aspect of the embodiment of thepresent invention, FIG. 2 is a block diagram of the position detectioncircuit of FIG. 1, FIG. 3 explains the servo signals, FIG. 4 is aflowchart explaining head switching, and FIG. 5 explains the headswitching operation.

[0046] As shown in FIG. 1, the magnetic disk drive 1 comprises themagnetic disk 2 and magnetic heads 3 a through 3 d. Servo signals areembedded in each sector of the data track in this magnetic disk 2. Asshown in FIG. 3, the servo signal comprises the servo mark signal usedto show the servo signal, a track number that shows the track number,and a two-phase servo signal comprising position signals PosA, PosB,PosC, and PosD.

[0047] Magnetic heads 3 a through 3 d read and write information from/onthe magnetic disk 2. The spindle motor 4 rotates magnetic disk 2. Thevoice coil motor 5 positions magnetic heads 3 a through 3 d to a desiredtrack of magnetic disk 2. The servo gate generator 6 produces the servogate signal with a servo signal period Ts. In response to the servo gatesignal, the position detection circuit 7 demodulates the servo signalfrom magnetic heads 3 a through 3 d into position signal.

[0048] The read-write circuit 8 demodulates read signal from magneticheads 3 a through 3 d and sends write data to magnetic heads 3 a through3 d. The VCM drive circuit 9 drives the voice coil motor 5. The SPMdrive circuit 10 drives the spindle motor 4.

[0049] The micro-controller 11 comprises a microprocessor, an analog todigital converter and a digital to analog converter, and reads positionsignals in response to the servo gate signal. The controller 11calculates the current head position from the position signal andcreates a current indication value in response to the distance from thetarget position.

[0050] The ROM 12 stores the programs and data required formicro-controller 11 processing. The hard disk controller 13 controls theinterface with higher-level computers. The RAM 14 is the memory used bythe hard disk controller 13. The address-data bus 15 connects the harddisk controller 13, the ROM 12, the micro-controller 11, the positiondetection circuit 7, the read-write circuit 8, the VCM drive circuit 9,and the SPM drive circuit 10 and exchanges data.

[0051] Details of the position detection circuit will now be explainedwith reference to FIG. 2.

[0052] As shown in FIG. 2, the servo gate generator 6 comprises a timesetting register 20, a counter 21, a comparison unit 22, and a gategeneration unit 23. The time setting register 20 sets the time at whichthe servo gate will be generated from the micro-controller 11. Thecounter 21 counts the reference clock. The comparison unit 22 comparesthe time set in register 20 and the value of the counter 21 and producesa matched output when the two match. The comparison unit 22 sends resetdata to the counter 21 when the set time and the counted value match. Inresponse to the matched output from the comparison unit 22, the gategeneration unit 23 generates a servo gate signal.

[0053] The position detection circuit 7 comprises a head selection unit25, a servo mark detection unit 26, a position signal detection unit 27,and a position information register 28. In response to a head switchingsignal from the micro-controller 11, the head selection unit 25 selectsread output from the specified magnetic head. In response to a servogate signal, the servo mark detection unit 26 detects the servo markfrom the read signal for the head. In response to the servo gate signaland servo mark detection signal, the position signal detection unit 27demodulates the servo signal from the read signal for the head into aposition signal. The position information register 28 stores thedemodulated position information.

[0054] When the servo mark detection unit 26 has detected the servomark, the micro-controller 11, in response to the servo interruptiongenerated by the servo mark detection unit 26, processes servo control.That is, in response to servo interruption, the micro-controller 11reads the position information from the position information register28. Then, in response to the position information, the micro-controller11 calculates the command current value. Furthermore, themicro-controller 11 sends the command current value to the VCM drivecircuit 9.

[0055] Memory 16 is connected to this micro-controller 11. The memory 16stores the time discrepancy that shows the servo gate time discrepanciesbetween each magnetic head and the standard head. Here, the standardhead is head 0. The discrepancies between the servo gate times for eachhead 1, 2, and 3, and the standard head 0 are stored. For example, asshown in FIG. 5, the discrepancy between the servo gate times of head 1and head 0 is Tb.

[0056] The operation of the circuit in FIG. 2 will now be explained. Thecounter 21 calculates the reference clock. The comparison unit 22compares the time set in register 20 with the value calculated bycounter 21. When the time set in register 20 matches the valuecalculated in counter 21, a match signal is sent to the gate generationunit 23. When the comparison unit 22 detects a match it resets counter21.

[0057] The gate generation unit 23, in response to the match signal,generates a servo gate signal with the reference clock timing. The servomark detection unit 26 detects the servo mark (refer to FIG. 3) from thedata output from the head in response to the servo gate signal. Theservo mark detection unit 26 cues the position signal detection unit 27to detect the position in response to the servo mark detection. Inaddition, the servo mark detection unit 26 sends a servo interruption tothe micro-controller 11.

[0058] The position signal detection unit 27 demodulates the positionsignal (refer to FIG. 3) from the data read from the head and sets thisin the position information register 28. The micro-controller 11 thatreceived the servo interruption starts servo processing. That is, themicro-controller 11 reads the position information stored in theposition information register 28 and calculates the deviation from thetarget position. Also, the micro-controller 11 creates a currentindication value to eliminate the deviation, and then sends the currentindication value to the VCM drive circuit 9.

[0059] Head switching process will be explained with reference to FIG.4.

[0060] (S1) When the micro-controller (hereinafter referred to as theMCU) 11 receives a head switching command, it reads the servo gate timediscrepancy Ta between the current head and the standard head frommemory 16. Next, the MCU 11 reads the servo gate time discrepancy Tbbetween the head to which switching is directed and the standard headfrom memory 16.

[0061] (S2) The MCU 11 calculates the time difference Td by calculating(Ta−Tb).

[0062] (S3) The MCU 11 determines whether or not the time difference Tdis larger than the servo signal period Ts. When the time difference Tdis larger than the period Ts, the interval between servo gate signalswill be smaller than the period Ts. This means that while the servoperiod Ts is not being reached, servo interruption will be generated andMCU 11 processing may not occur in time. Therefore, when the timedifference Td is not greater than the period Ts, the servo gate signalwill be delayed by one sample period. In other words Td will beconverted to (Td+Ts).

[0063] (S4) Next, the MCU 11 sets the time difference Td in the servogate time setting register 20 shown in FIG. 3 at the servo interruptiontiming. This causes the comparison unit 22 to generate matched outputafter the time difference Td has passed. This in turn causes the servogate generation unit 23 to then generate a servo gate signal after thetime difference Td has passed.

[0064] (S5) Next, the MCU 11 switches heads. That is, the MCU 11 sendsthe number of the head to which switching is directed to the headselection unit 25. This causes head switching.

[0065] (S6) When the MCU 11 detects servo interruption, it sets thesample period Ts in the servo gate time setting register 20. Processingthen ends.

[0066] In this way, the servo gate signals are synchronized at the timeof the position signal for the head to which switching is directed.Therefore, the time discrepancies between position signals for all headsare stored and the time difference between the current head and the headto which switching is directed is calculated. The time at which theservo gate signal is generated is then synchronized with this timedifference. FIG. 5 shows the relationship between the servo signals foreach head when heads are switched from head 0 to head 1 and the servogate signals. In this example, the time discrepancy for head 0 Ta is “0”and the time discrepancy between head 0 and head 1 is Tb. The servo gatesignal shown is for when the time difference Td is smaller than thesample period Ts.

[0067] In the diagram, the interval between servo gate signals after thehead switching command arrives is converted to Td+Ts and synchronizedwith the position signal for head 1. Thereafter, the interval betweenservo gate signals returns to the sample period Ts.

[0068] Thus, when head switching occurs, the time difference between thedetection time for the servo signal for the head to which switching isdirected and the detection time for the servo signal for the head fromwhich switching originates is calculated, and the time at which theservo gate signal is generated is synchronized with the servo signaldetection time for the head to which switching is directed. Therefore,even if heads are switched, the servo signal can be detected immediatelyfrom the head to which switching is directed.

[0069]FIG. 6 gives a relational view of servo gate signals in a secondaspect of the embodiment of the present invention. FIG. 6 shows headswitching from head 0 to head 1. In the examples in FIGS. 4 and 5, thetime difference Td was calculated to make it the same as or higher thanthe sample period Ts. However, the example shown in FIG. 6 uses the timedifference Td as is.

[0070] That is, the processing in Step S3 of FIG. 4 does not take place.Thus, when the time difference Td is smaller than the sample period Ts,as shown in FIG. 6, the servo gate signal is generated before one sampleinterval Ts has passed in the synchronization operation for servo gatesignals that occurs after the head switching command has been received.This causes servo interruption to be generated. However, when theprocessing capability of the MCU 11 is high, this servo interruption canbe processed. Also, as will be explained below, the MCU 11 can be set toignore this interruption.

[0071]FIG. 7 is a block diagram of a third aspect of the embodiment ofthe present invention. FIG. 7 shows a modification of the positiondetection circuit of FIG. 2. In FIG. 7, the parts that are the same asparts shown in FIG. 2 are shown using the same codes.

[0072] The head number setting unit 30 sets the number of the head to beoperated from the MCU 11. The register 31 stores the head number set inthe head number setting unit 30. The comparison unit 32 compares thehead number in the head number setting unit 30 and the head number inthe register 31. The comparison unit 32 deems there to be a headswitching cue when the two head numbers do not match and cues theregister 31 to store the head number of the head number setting unit 30.

[0073] When the two head numbers do not match, the comparison unit 32cues the calculation unit 33 to calculate the time difference. When thetwo head numbers do not match, the comparison unit 32 cues the selectionunit 34 to select the output of the calculation unit 33.

[0074] As with memory 16 in FIG. 2, the gate time interval memory 36stores the servo gate time discrepancies between heads 1 and 2 and thestandard head. The calculation unit 33 reads the gate time intervalmemory 36 using the head number in the head number setting unit 30 thenobtains the time discrepancy Tb for the head to which switching isdirected. The calculation unit 33 reads the gate time interval memory 36and obtains the current head time discrepancy Ta by using the headnumber in the register 31. The calculation unit 33 then subtracts timediscrepancy Tb from time discrepancy Ta to obtain the time differenceTd.

[0075] The sample period memory 35 stores the sample period Ts for theservo gate signal. In response to the unmatched output of the comparisonunit 32, the selection unit 34 selects the time difference Td from thecalculation unit 33 and, in response to a matched output of thecomparison unit 32, selects the sample period Ts of the sample periodmemory 35. The output of this selection unit 34 is entered into thecomparison unit 22 as the gate interval.

[0076] The operation of this circuit will now be explained. Thecomparison unit 32 compares the head number in the head number settingunit 30 with the head number in the register 31. When these head numbersdo not match, the comparison unit 32 deems this to be a head-switchingcue. The comparison unit 32 cues the calculation unit 33 to calculatethe time difference.

[0077] When the two head numbers do not match, the comparison unit 32cues the calculation unit 33 to calculate the time difference. When thetwo numbers do not match, the comparison unit also cues the selectionunit 34 to select the output of the calculation unit 33.

[0078] The calculation unit 33 reads the gate time interval memory 36using the head number in the head number setting unit 30 to obtain thetime discrepancy Tb for the head to which switching is directed. Thecalculation unit 33 reads the gate time interval memory using the headnumber of the register 31 to obtain the time discrepancy Ta for thecurrent head. Then, the calculation unit 33 subtracts time discrepancyTb from time discrepancy Ta to obtain the time difference Td.

[0079] A “no match” comparison in comparison unit 32 will cause theselection unit 34 to select the time difference Td in calculation unit32 as the gate interval. As in FIG. 2, the comparison unit 22 comparesthe time set in the register 20 with the value calculated in counter 21.When the time set in register 20 and the value calculated in counter 21match, the comparison unit 22 sends a match signal to the gategeneration unit 23. The comparison unit 22 also resets counter 21 when amatch is detected.

[0080] In response to a match signal, the gate generation unit 23generates a servo gate signal with the reference clock timing. Inresponse to the servo gate signal, the servo mark detection unit 26detects the servo mark (refer to FIG. 3) from the data read from thehead. In response to the detection of the servo mark, the servo markdetection unit 26 cues the position signal detection unit 27 to detect aposition. In addition, the servo mark detection unit 26 sends a servointerruption to the micro-controller 11.

[0081] The position signal detection unit 27 demodulates the positionsignal (refer to FIG. 3) from the data read from the head and sets thisinto the position information register 28. The micro-controller 11 thatreceived the servo interruption starts servo processing. That is, themicro-controller 11 reads the position information from the positioninformation register 28 and calculates the deviation from the targetposition. The micro-controller 11 then creates a current indicationvalue to eliminate this deviation and send the current indication valueto the VCM drive circuit 9.

[0082] On the other hand, a “no match” signal in the comparison unit 32will cause the register 31 to be updated and the register 31 will thenstore the head number from the head number setting unit 30. This in turnwill cause the comparison unit 32 to generate a match signal and theselection unit 34 to switch to the sample period memory 35. This willresult in the selection unit 34 sending the sample period Ts as the gateinterval.

[0083] Thus, the functions of the MCU 11 firmware in FIG. 2 can also beachieved through hardware.

[0084]FIG. 8 is a flowchart for processing in a fourth aspect of theembodiment of the present invention and shows the processing involved inhead switching.

[0085] (S10) When the MCU 11 receives a head switching command, it readsthe servo gate time discrepancy Ta between the current and standardheads from memory 16. Next, the MCU 11 reads the servo gate timediscrepancy Tb between the head to which switching is directed and thestandard head from memory 16.

[0086] (S11) The MCU 11 calculates the time difference by calculating(Ta−Tb).

[0087] (S12) The MCU determines whether or not the time difference Td islarger than the servo signal period Ts. When the time difference Td isnot larger than the period Ts, the interval between servo gate signalsis smaller than period Ts. Thus, while the servo period Ts is notreached, a servo interruption will be produced and multipleinterruptions may occur during positioning by the MCU 11.

[0088] (S13) When the time difference Td is larger than the period Ts,the MCU 11 will start VCM processing (servo positioning) in response tothe servo interruption. It will then start head switching and endinterruption processing.

[0089] (S14) Conversely, when the time difference Td is not larger thanthe period Ts, the MCU 11 will inhibit servo interruptions and willstart head switching. Also, the MCU 11 will clear the interruption flagand permit interruptions. The MCU 11 will then end interruptionprocessing.

[0090] Thus, as explained in FIG. 6, the MCU 11 will inhibitinterruptions when the time difference Td is less than the servo signalperiod Ts. That is, the MCU 11 is able to find out the time differenceTd and the period Ts in advance when heads are switched. Therefore, whenthe time difference Td is less than the period Ts, in this sample,positioning control will not occur, interruption processing will endimmediately, and the next interruption will be awaited.

[0091] Next, it is necessary to measure these types of head timediscrepancies in advance. This can be done using a measurement deviceoutside the disk device or a program within the disk unit.

[0092]FIG. 9 is a block diagram concerning the measurement of timediscrepancies between heads. FIG. 9 is a block diagram of the externaldevice for measuring the time discrepancies for each head in themagnetic disk device.

[0093] The external measurement device comprises the first positiondetection circuit 7-1, the second position detection circuit 7-2, a headselector 37, and a control circuit 38. The data read from the standardhead 0 is input into the first position detection circuit 7-1. The dataread from heads 1, 2, or 3 selected by the head selector 37 is inputinto the second position detection circuit 7-2.

[0094] During measurement, the control circuit 38 applies a servo gatesignal that is always on to the first position detection circuit 7-1 andthe second position detection circuit 7-2. This causes the servo markdetection unit of the first position detection circuit 7-1 to find aservo mark from the data read from head 0 and, upon detection, to outputa servo mark detection pulse to the control circuit 38.

[0095] On the other hand, the servo mark detection unit in the secondposition detection circuit 7-2 finds the servo mark from the data readfrom the selected head (for example, 1) and, upon detection, outputs aservo mark detection pulse to the control circuit 38.

[0096] The control circuit 38 can measure the time discrepancy betweenthe targeted head (for example, 1) and the standard head 9 by measuringthe time between the two detection pulses. By appropriate selection ofthe head selector 37, the time discrepancy between head 2 and thestandard head 0 and the time discrepancy between head 3 and the standardhead 0 can be measured. These measurements are recorded in the memory 16of FIG. 2 or in the memory of FIG. 7. Also, when the power is on, thesemeasurements can be written to the magnetic disk track position firstaccessed by the head.

[0097]FIG. 10 is a flowchart for the measurement of time discrepanciesbetween heads. FIG. 10 is a flowchart showing how the MCU in themagnetic disk unit measures time discrepancies.

[0098] (S20) The MCU 11 causes the free-run timer to operate and causesthe magnetic disk to be on track with head 0. Here, the servo gatesignal is always left on.

[0099] (S21) When the above position detection circuit 8 detects theservo mark, a servo interruption will be reported to the MCU 11. The MCU11 records the free-run timer value (T0) immediately after the servointerruption.

[0100] (S22) The MCU 11 switches heads but does not synchronize withposition signals or include the position.

[0101] Therefore, it cannot control positioning. Here, the currentsupplied to the VCM when it is on-track with head 0 is maintained. Thisenables the current that runs when a constant bias has just beencancelled to flow to the VCM. When the VCM position is movedsubstantially, movement towards the edge of the magnetic disk (areawhere no position signals are written) is prevented. The head selectionpart 25 switches to the measurement head (for example, 1).

[0102] (S23) The MCU 11 again turns on the servo gate signal andresynchronises the position detection circuit (demodulation circuit).

[0103] (S24) When the servo mark is detected, the above positiondetection circuit 7 reports a servo interruption to the MCU 11. The MCU11 then records the value for the free-run timer (T1) immediately afterthe servo interruption.

[0104] (S25) The MCU 11 calculates the time discrepancy from theremainder when the difference between the two timer values (T1−T0) isdivided by the sample period Ts.

[0105] This is done for each head 1, 2, and 3, to be measured. Thus, thetime discrepancies for each head are measured by the controller withinthe magnetic disk device. These measurements are stored in the memory 16and recording part 36.

[0106]FIG. 11 explains a fifth aspect of the embodiment of the presentinvention.

[0107] During positioning control, the current is calculated using aconstant sample period Ts. However, when heads are switched, thisperiod, like Td, is a different value to the sample period Ts. So, whenheads are switched, the wave height value of the current flowing in theVCM is revised. That is, as shown in FIG. 11, when heads are switchedthe wave-form value u is determined by the following equation. u0 is thevalue calculated for the VCM current.

u=u0×Ts/Td

[0108] Thus, revision of the wave height in response to the samplinginterval enables smoother VCM control. When the constant bias current issmall, the above equation is used but when the bias current is large,the above equation is applied to the current remaining after the biascurrent is taken away.

[0109] In addition to the above aspect of the embodiment of the presentinvention, the following types of modification are also possible.

[0110] (1) The storage disk device has been explained as a magnetic diskdevice but this method can also apply to magneto-optical disk devices,optical disk devices, and other storage disk devices.

[0111] (2) This method has been explained for a device in which twodisks are loaded but can also apply to devices in which one disk isloaded and also to devices in which there are two or more heads.

[0112] Some different aspects of the embodiment of the present inventionhave been explained above but a number of modifications are possiblewithin the main scope of the present invention. These are not excludedfrom the scope of the present invention.

INDUSTRIAL APPLICABILITY

[0113] As explained above, the present invention can provide thefollowing:

[0114] (1) Because, in response to a head switching command, thedetection time for a detection signal is synchronized with the time ofthe head position signal for the head in which switching is directed,even if the position signal search operation is omitted when heads areswitched, the position signal for the head in which switching isdirected can be detected.

[0115] (2) Therefore, the time involved in switching heads can bereduced and fast head switching operations are enabled.

What is claimed is:
 1. A head positioning control method for a storagedisk device which comprises; a storage disk that stores a positionsignal; a plurality of heads that read information from the said storagedisk; an actuator that moves the said head; and a control circuit thatpositions the said head based on the position signal read from the saidstorage disk using a selected head, said method comprising: a step ofsynchronizing a time of a detection signal for detecting said positionsignal with a time of said position signal read by head to whichswitching is directed, in response to a head switching cue,; and a stepof reading said position signal for said head in response to saidsynchronized detection signal and positioning the said head according tosaid read position signal.
 2. The head positioning control method for astorage disk device of claim 1 , wherein said synchronizing stepcomprises: a step of determining a time at which the head to which saidswitching is directed reads said position signal, in response to saidhead switching cue; and a step of synchronizing the time of saiddetection signal with said determined time.
 3. The head positioningcontrol method for a storage disk device of claim 2 , wherein said timedetermining step comprises a step for determining said time of a valuegreater than one sample period for said positioning control.
 4. The headpositioning control method for a storage disk device of claim 2 whereinsaid time determining step includes a step for reading the time read bythe head to which said switching is directed from a memory for storingthe time at which the position signal for each head is read.
 5. The headpositioning control method for a storage disk device of claim 2 ,wherein said time determining step comprises a step for determining thetime difference between the detection time of said position signal forthe head from which said switching originates and the detection time ofsaid position signal for the head to which said switching is directed,and wherein said synchronizing step comprises a step for time-shiftingthe said detection signal for said time difference.
 6. The headpositioning control method for a storage disk device of claim 5 ,wherein said time determining step comprises: a step of determining thedetection time of said position signal for the head from which saidswitching originates; a step of determining the detection time of saidposition signal for the head to which said switching is directed; and astep of determining the time difference between the two detection times.7. The head positioning control method for a storage disk device ofclaim 1 , wherein said positioning step comprises: a step ofcalculating, in response to said head switching cue, the time differencebetween the detection time for the head from which the said switchingoriginates and the detection time for the head to which said switchingis directed; a step of determining whether or not the said timedifference is shorter than one sample interval; and a step of inhibitingpositioning in response to said detection signal when said timedifference is shorter than one sample interval.
 8. A head positioningcontrol device for a storage disk apparatus, comprising; a storage diskthat stores position signals; a plurality of heads for readinginformation from said storage disk; an actuator for moving said heads;and a control circuit for positioning said heads based on the positionsignal read from the said storage disk by a selected head, wherein saidcontrol circuit comprises: a synchronization circuit that, in responseto a head switching cue, synchronizes the time of the detection signalfor detecting said position signal with the time of the position signalread by the head from which switching originates, and a processingcircuit that, in response to said synchronized detection signal, readsthe said position from the said head and, in response to the readposition signal, positions the said head.
 9. The head positioningcontrol device for a storage disk apparatus of claim 8 , wherein saidsynchronization circuit comprises: a circuit for determining the time atwhich the head from which said switching is directed reads said positionsignal in response to said head switching cue, and synchronizing time ofsaid detection signal with said determined time.
 10. The headpositioning control device for a storage disk apparatus of claim 9 ,wherein said synchronization circuit comprises a circuit that determinessaid time the value of which is greater than one sample period for saidpositioning control.
 11. The head positioning control device for astorage disk apparatus of claim 9 , wherein said synchronization circuitcomprises memory for storing the times at which the position signals ofeach head are read.
 12. The head positioning control device for astorage disk apparatus of claim 9 , wherein said synchronization circuitcomprises: a circuit that determines the time difference between thedetection time of said position signal for the head used prior toswitching and the detection time of said position signal for the head towhich said switching is directed; and a circuit that shifts in time saiddetection signal by that time difference.
 13. The head positioningcontrol device for a storage disk apparatus of claim 11 , wherein saidsynchronization circuit comprises a circuit for determining from saidmemory the detection time of said position signal for the head usedprior to said switching and the detection time of the said positionsignal for the head to which said switching is directed, and calculatingthe time difference between the two detection times.
 14. The headpositioning control device for a storage disk apparatus of claim 8 ,wherein said processing circuit comprises a circuit that determineswhether or not the time difference between the detection time for headused prior to said switching and the detection time for the head towhich said switching is directed is less than one sample interval andthat, when said time difference is shorter than one sample interval,inhibits positioning in response to said detection signal.